Heat a grill pan over medium heat. Add peaches and grill until outsides are caramelized.

Meanwhile, preheat oven to 350 degrees Fahrenheit. Combine balsamic vinegar and brown sugar in a small saucepan over medium-low heat. Let simmer until vinegar reduces and mixture is thick and syrupy.

Transfer peaches to a lined baking sheet. Brush with balsamic glaze and bake for 15 minutes.

Whisk all dressing ingredients together.

Plate each salad with lettuce, peaches, walnuts, and crumbled feta. Drizzle with vinaigrette and serve.